Individuals with mental illness (MI), suffering from such conditions as schizophrenia, bipolar disorder, major depression, and/or substance abuse, may also present with chronic medical conditions. Yet our understanding of their use of non-psychiatric health services is very limited. MI patients face numerous barriers to access and adequately utilize health services, including - but not encompassing - financial barriers, and difficulties understanding and being compliant with medical recommendation or treatment. Additionally, given the priority assigned to the management of psychiatric conditions, medical conditions may receive lesser attention in MI than in non-MI patients. Consequently, MI patients are likely to under use much needed health services, resulting in poor prevention and management of chronic diseases and greater morbidity and mortality than that observed in non-MI patients. This is particularly true of cancer, because early detection and receipt of adequate treatment and follow-up care are some of the most important determinants of cancer outcomes. Despite these important differences in patterns of health services utilization, and potential outcomes, MI patients have seldom been identified as a vulnerable subgroup of the population in the disparities literature. The proposed studies will describe patterns of breast cancer screening, diagnosis, treatment, and surveillance in MI and non-MI populations in Ohio, through secondary data analysis. We will focus on female breast cancer because of its high prevalence, and its amenability to screening. Given the significant representation of MI patients in the Medicaid population, we will be using state Medicaid data linked with the Ohio Cancer Incidence Surveillance System (OCISS). First, we will compare receipt of mammography by Medicaid-insured women between those with and without MI. Next, among those diagnosed with incident breast cancer, we will determine whether MI is associated with a) breast cancer stage at presentation;b) receipt of definitive primary and adjuvant treatment in early breast cancer patients;and c) receipt of guideline surveillance after initial treatment for non-metastatic breast cancer. By limiting our studies to Medicaid beneficiaries, we will be able to compare outcomes between MI and non-MI patients who share comparable socio-economic status and various other types of barriers in accessing care. The proposed studies will pave the way for more detailed evaluations aimed at identifying specific factors hindering adequate use of medical services by MI patients, and at developing interventions to improve strategies of cancer prevention and control in this doubly disadvantaged patient population. As well, these studies will raise awareness in the health care provider and research communities relative to the vulnerabilities associated with MI status, and the importance of special considerations in the design of case management programs for MI patients. Medicaid beneficiaries with mental illness represent a doubly disadvantaged population, given the vulnerabilities associated with each of Medicaid status and mental illness, yet studies relevant to this population have been absent from the disparities literature. By comparing female breast cancer-related care process and outcome measures among Medicaid-insured women between those with and without mental illness, the proposed studies will pave the way for more detailed evaluations aimed at identifying specific factors hindering adequate use of medical services by MI patients, and at developing interventions to improve strategies of cancer prevention and control in this patient population.